Zoom lens and imaging apparatus

ABSTRACT

The zoom lens consists of, in order from an object side: a positive first lens group that does not move during zooming; a middle group that consists of two or more movable lens groups moving during zooming; and a subsequent group that has a lens group including a stop at a position closest to the object side. The middle group has at least two negative movable lens groups. At least one negative movable lens group in the middle group includes at least one negative LN lens which satisfies predetermined conditional expressions relating to the refractive index, the Abbe number, and the partial dispersion ratio.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 toJapanese Patent Application No. 2018-154923, filed on Aug. 21, 2018. Theabove application is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a zoom lens and an imaging apparatus.

2. Description of the Related Art

In the related art, as a zoom lens used in broadcast cameras, movieimaging cameras, digital cameras, and the like, there is known a type inwhich a lens group having a positive refractive power is disposed to beclosest to the object side, a movable lens group moves to the image sideduring zooming, and the total length of the lens system remainsunchanged during zooming. For example, JP2017-078770A and JP2017-083563Adescribe the above-mentioned type zoom lenses each having five or sixlens groups.

SUMMARY OF THE INVENTION

The zoom lenses used in the cameras are required to have highperformance and small aberration fluctuation during zooming. In order toensure the zoom ratio, it is necessary to increase the refractive powerof the movable lens group, which tends to increase fluctuation inchromatic aberration and fluctuation in spherical aberration duringzooming. In order to suppress fluctuation in chromatic aberration duringzooming, it is desirable to suppress chromatic aberration independentlyof the movable lens group and the lens group which has a positiverefractive power and is closest to the object side. In such a case,particularly, it is important to arrange refractive powers and selectthe material of the lenses of the movable lens group for suppressingfluctuation in secondary chromatic aberration.

On the other hand, in a case where fluctuation in spherical aberrationduring zooming is not sufficiently suppressed, a problem arises in thatthe F number can not be reduced at the telephoto end. In the lenssystems described in JP2017-078770A and JP2017-083563A, the suppressionof fluctuation in spherical aberration during zooming is not sufficient,and there is room for improvement.

The present invention has been made in view of the above circumstances.According to an embodiment of the present invention, it is an object toprovide a zoom lens having high optical performance by suppressingfluctuation in chromatic aberration and fluctuation in sphericalaberration during zooming and an imaging apparatus comprising the zoomlens.

The specific means for achieving the object includes the followingaspects.

<1> A zoom lens consisting of, in order from an object side to an imageside: a first lens group that remains stationary with respect to animage plane during zooming and has a positive refractive power; a middlegroup that consists of two or more movable lens groups moving along anoptical axis by changing a distance between groups adjacent to eachother during zooming; and a subsequent group that has a lens groupincluding a stop at a position closest to the object side, where atleast two movable lens groups in the middle group each have a negativerefractive power, where the at least one movable lens group having thenegative refractive power in the middle group includes at least one LNlens which is a negative lens, and where assuming that a refractiveindex of the LN lens at a d line is Ndn, an Abbe number of the LN lensbased on the d line is vdn, and a partial dispersion ratio of the LNlens between a g line and an F line is θgFn, the LN lens satisfiesConditional Expressions (1), (2), (3), and (4) represented by1.72<Ndn<1.8  (1),43<νdn<57  (2),0.6355<θgFn+0.001625×νdn<0.66  (3), and2.21<Ndn+0.01×νdn  (4).

<2> The zoom lens according to <1>, where the movable lens group, whichhas the negative refractive power in the middle group, closer to theobject side than the movable lens group, which has the negativerefractive power and is closest to the image side in the middle group,includes the LN lens, and where assuming that a focal length of themovable lens group which has the negative refractive power in the middlegroup and includes the LN lens, which has a strongest negativerefractive power among the LN lenses, which are included in the movablelens group having the negative refractive power in the middle group andbeing located to be closer to the object side than the movable lensgroup, which has the negative refractive power and is closest to theimage side in the middle group, is fA, and a focal length of the movablelens group, which has the negative refractive power and is closest tothe image side in the middle group, is fB, Conditional Expression (5) issatisfied, which is represented by0.6<fB/fA<4.5  (5).

<3> The zoom lens according to <1> or <2>, where the movable lens group,which has the negative refractive power in the middle group, closer tothe object side than the movable lens group, which has the negativerefractive power and is closest to the image side in the middle group,includes the LN lens, and where assuming that a focal length of themovable lens group which has the negative refractive power in the middlegroup and includes the LN lens, which has a strongest negativerefractive power among the LN lenses, which are included in the movablelens group having the negative refractive power in the middle group andbeing located to be closer to the object side than the movable lensgroup, which has the negative refractive power and is closest to theimage side in the middle group, is fA, and a focal length of the LNlens, which has the strongest negative refractive power, among the LNlenses, which are included in the movable lens group having the negativerefractive power in the middle group, is fLNm, Conditional Expression(6) is satisfied, which is represented by0.5<fLNm/fA<40  (6).

<4> The zoom lens according to any one of <1> to <3>, where the at leastone movable lens group in the middle group includes a cemented lens inwhich at least one LN lens and at least one positive lens are cemented.

<5> The zoom lens according to <4>, where assuming that an Abbe numberof the at least one LN lens of the cemented lens based on the d line isνdcn, and an Abbe number of at least one positive lens of the cementedlens based on the d line is νdcp, at least one of the cemented lensessatisfies Conditional Expression (7) represented by18<νdcn−νdcp<35  (7).

<6> The zoom lens according to any one of <1> to <5>, where the movablelens group having the strongest negative refractive power among themovable lens groups having the negative refractive powers in the middlegroup includes the LN lens.

<7> The zoom lens according to any one of <1> to <6>, where focusing isperformed by moving at least a part of lenses in the first lens groupalong the optical axis.

<8> The zoom lens according to any one of <1> to <7>, where the movablelens group closest to the image side in the middle group has a negativerefractive power.

<9> The zoom lens according to <8>, where the middle group consists ofthe two movable lens groups having the negative refractive powers, andwhere the subsequent group consists of a lens group which remainsstationary with respect to the image plane during zooming and has apositive refractive power.

<10> The zoom lens according to <8>, where the middle group consists ofthe two movable lens groups having the negative refractive powers, andwhere the subsequent group consists of, in order from the object side tothe image side, a lens group, which moves along the optical axis bychanging a distance between the groups adjacent to each other duringzooming and has a positive refractive power, and a lens group whichremains stationary with respect to the image plane during zooming andhas a positive refractive power.

<11> The zoom lens according to <8>, where the middle group consists of,in order from the object side to the image side, the movable lens grouphaving a positive refractive power and the two movable lens groupshaving the negative refractive powers, and where the subsequent groupconsists of a lens group which remains stationary with respect to theimage plane during zooming and has a positive refractive power.

<12> The zoom lens according to <8>, where the middle group consists ofthe three movable lens groups having the negative refractive powers, andwhere the subsequent group consists of a lens group which remainsstationary with respect to the image plane during zooming and has arefractive power.

<13> The zoom lens according to <8>, where the middle group consists ofthe four movable lens groups having the negative refractive powers, andwhere the subsequent group consists of a lens group which remainsstationary with respect to the image plane during zooming and has apositive refractive power.

<14> The zoom lens according to any one of <1> to <13>, where the LNlens further satisfies Conditional Expression (2-1) represented by45<νdn<55  (2-1).

<15> The zoom lens according to any one of <1> to <14>, where the LNlens further satisfies Conditional Expression (3-1) represented by0.637<θgFn+0.001625×νdn<0.65  (3-1).

<16> The zoom lens according to any one of <1> to <15>, where the LNlens further satisfies Conditional Expression (4-1) represented by2.21<Ndn+0.01×νdn<2.33  (4-1).

<17> The zoom lens according to <2>, where Conditional Expression (5-1)is satisfied, which is represented by2<fB/fA<4  (5-1).

<18> The zoom lens according to <3>, where Conditional Expression (6-1)is satisfied, which is represented by0.5<fLNm/fA<4  (6-1).

<19> An imaging apparatus comprising the zoom lens according to any oneof <1> to <18>.

In the present specification, it should be noted that the terms“consisting of ˜” and “consists of ˜” mean that the lens may include notonly the above-mentioned elements but also lenses substantially havingno refractive powers, optical elements, which are not lenses, such as astop, a filter, and a cover glass, and mechanism parts such as a lensflange, a lens barrel, an imaging element, and a camera shakingcorrection mechanism.

In addition, the term “˜ group that has a positive refractive power” inthe present specification means that the group has a positive refractivepower as a whole. Likewise, the “˜ group having a negative refractivepower” means that the group has a negative refractive power as a whole.The term “a lens having a positive refractive power” and the term “apositive lens” are synonymous. The term “a lens having a negativerefractive power” and the term “negative lens” are synonymous. The “lensgroup” is not limited to a configuration using a plurality of lenses,but may consist of only one lens. Further, regarding the “one lensgroup”, a lens group in which the distance in the direction of theoptical axis between the groups adjacent to each other changes duringzooming is regarded as “one lens group”. That is, in a case where thelens group is divided at intervals changing during zooming, the lensgroup included in one division is regarded as one lens group.

A compound aspheric lens (a lens which is integrally composed of aspherical lens and a film having an aspheric shape formed on thespherical lens, and functions as one aspheric lens as a whole) is not beconsidered as a cemented lens, and is treated as a single lens. The signof the refractive power and the surface shape of the lens surface of alens including an aspheric surface are considered in terms of theparaxial region unless otherwise noted.

The “focal length” used in a conditional expression is a paraxial focallength. The values used in the conditional expressions are values in thecase of using the d line as a reference in a state where the object atinfinity is in focus. The partial dispersion ratio θgF between the gline and the F line of a certain lens is defined by θgF=(Ng−NF)/(NF−NC),where Ng, NF, and NC are the refractive indices of the lens at the gline, the F line, and the C line. The “d line”, “C line”, “F line”, and“g line” described in the present specification are emission lines. Thewavelength of the d line is 587.56 nm (nanometers) and the wavelength ofthe C line is 656.27 nm (nanometers), the wavelength of F line is 486.13nm (nanometers), and the wavelength of g line is 435.84 nm (nanometers).

According to an embodiment of the present invention, it is possible toprovide a zoom lens having high optical performance by suppressingfluctuation in chromatic aberration and fluctuation in sphericalaberration during zooming and an imaging apparatus comprising the zoomlens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a cross-sectional view of aconfiguration of a zoom lens according to an embodiment of the presentinvention and a movement locus corresponding to the zoom lens of Example1 of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of thezoom lens and rays shown in FIG. 1.

FIG. 3 is a diagram illustrating a cross-sectional view of aconfiguration of a zoom lens according to Example 2 of the presentinvention and a movement locus thereof.

FIG. 4 is a diagram illustrating a cross-sectional view of aconfiguration of a zoom lens according to Example 3 of the presentinvention and a movement locus thereof.

FIG. 5 is a diagram illustrating a cross-sectional view of aconfiguration of a zoom lens according to Example 4 of the presentinvention and a movement locus thereof.

FIG. 6 is a diagram illustrating a cross-sectional view of aconfiguration of a zoom lens according to Example 5 of the presentinvention and a movement locus thereof.

FIG. 7 is a diagram of aberrations of the zoom lens of Example 1 of thepresent invention.

FIG. 8 is a diagram of aberrations of the zoom lens of Example 2 of thepresent invention.

FIG. 9 is a diagram of aberrations of the zoom lens of Example 3 of thepresent invention.

FIG. 10 is a diagram of aberrations of the zoom lens of Example 4 of thepresent invention.

FIG. 11 is a diagram of aberrations of the zoom lens of Example 5 of thepresent invention.

FIG. 12 is a schematic configuration diagram of an imaging apparatusaccording to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the zoom lens of the present invention willbe described in detail with reference to the drawings. FIG. 1 is across-sectional view illustrating a configuration and a movement locusof a zoom lens according to an embodiment of the present invention. FIG.2 is a cross-sectional view illustrating the lens configuration and therays in each state of the zoom lens. The examples shown in FIGS. 1 and 2correspond to the zoom lens of Example 1 to be described later. FIGS. 1and 2 each show a situation where the object at infinity is in focus,the left side thereof is an object side, and the right side thereof isan image side. FIG. 1 shows the wide-angle end state. In FIG. 2, theupper part labeled “WIDE-ANGLE END” indicates the wide-angle end state,the middle part labeled “MIDDLE” indicates the middle focal lengthstate, and the lower part labeled “TELEPHOTO END” indicates thetelephoto end state. FIG. 2 shows rays including on-axis rays wa andrays with the maximum angle of view wb at the wide-angle end state,on-axis rays ma and rays with the maximum angle of view mb at the middlefocal length state, and on-axis rays to and rays with the maximum angleof view tb at the telephoto end state.

Further, FIGS. 1 and 2 show an example in which, assuming that a zoomlens is applied to an imaging apparatus, an optical member PP of whichthe incident surface and the exit surface are parallel is disposedbetween the zoom lens and the image plane Sim. The optical member PP isa member assumed to include various filters, a prism, a cover glass,and/or the like. The various filters include, for example, a low passfilter, an infrared cut filter, and a filter that cuts a specificwavelength region. The optical member PP has no refractive power, andthe optical member PP may be configured to be omitted. Hereinafter,description will be given mainly with reference to FIG. 1.

The zoom lens of the present invention consists of, in order from theobject side to the image side along the optical axis Z, a first lensgroup G1, a middle group Gm, and a subsequent group Gs. The first lensgroup G1 is a lens group which remains stationary with respect to theimage plane Sim during zooming and has a positive refractive power. Themiddle group Gm consists of two or more movable lens groups which movealong the optical axis Z by changing the distance between groupsadjacent to each other during zooming. That is, the middle group Gmconsists of two or more movable lens groups that move along the opticalaxis Z with loci different from each other during zooming. At least twomovable lens groups in the middle group Gm each have a negativerefractive power. The subsequent group Gs has a lens group including anaperture stop St at the position closest to the object side.

By making the lens group closest to the object side as a lens grouphaving a positive refractive power, it is possible to shorten the totallength of the lens system (the distance from the lens surface closest tothe object side to the image plane Sim). As a result, there is anadvantage in achieving reduction in size. Further, the lens group, whichhas a positive refractive power and is closest to the object side, isconfigured to remain stationary during zooming. In such a configuration,the total length of the lens system does not change during zooming, andit is possible to reduce fluctuation in barycenter of the lens system.Thus, it is possible to improve the convenience at the time of imaging.Further, two or more movable lens groups having negative refractivepowers are disposed to be closer to the object side than the lens groupincluding the aperture stop St. Thereby, it is possible to disperse therefractive power of the negative movable lens group having a zoomingfunction. As a result, fluctuation in spherical aberration and thevariation of chromatic aberration during zooming can be reduced.Thereby, there is an advantage in achieving both small F number and highmagnification.

The zoom lens of the example shown in FIG. 1 consists of, in order fromthe object side to the image side, a first lens group G1 having apositive refractive power, a second lens group G2 having a negativerefractive power, a third lens group G3 having a negative refractivepower, and a fourth lens group G4 having a refractive power. Duringzooming, the first lens group G1 and the fourth lens group G4 remainwith respect to the image plane Sim. The second lens group G2 and thethird lens group G3 are movable lens groups that move along the opticalaxis Z by changing the distance between groups adjacent to each otherduring zooming. The aperture stop St is disposed to be closest to theobject side of the fourth lens group G4. The aperture stop St shown inFIG. 1 does not show its shape but shows its position in the directionof the optical axis. In the example shown in FIG. 1, the groupconsisting of the second lens group G2 and the third lens group G3corresponds to the middle group Gm, and the fourth lens group G4corresponds to the subsequent group Gs. In FIG. 1, the movement locus ofeach movable lens group during zooming from the wide-angle end to thetelephoto end under the movable lens group is schematically indicated bythe arrow.

In the example shown in FIG. 1, the first lens group G1 consists ofeleven lenses L1 a to L1 k in order from the object side to the imageside, and the second lens group G2 consists of six lenses L2 a to L2 fin order from the object side to the image side, the third lens group G3consists of two lenses L3 a and L3 b in order from the object side tothe image side, and the fourth lens group G4 consists of the aperturestop St and nine lenses L4 a to L4 i in order from the object side tothe image side. However, in the zoom lens of the present invention, thenumber of lens groups constituting the middle group Gm and thesubsequent group Gs, the number of lenses constituting each lens group,and the position of the aperture stop St may be set to be different fromthose in the example shown in FIG. 1.

In the zoom lens of the present invention, the at least one movable lensgroup having the negative refractive power in the middle group Gmincludes at least one LN lens LN which is a negative lens. Assuming thata refractive index of the LN lens LN at the d line is Ndn, an Abbenumber of the LN lens LN based on the d line is νdn, and a partialdispersion ratio of the LN lens LN between a g line and an F line isθgFn, the LN lens LN satisfies Conditional Expressions (1), (2), (3),and (4).1.72<Ndn<1.8  (1)43<νdn<57  (2)0.6355<θgFn+0.001625×νdn<0.66  (3)2.21<Ndn+0.01×νdn  (4)

Conditional Expressions (1), (2), (3) and (4) are conditionalexpressions relating to the material of the LN lens LN. By not allowingthe result of Conditional Expression (1) to be equal to or less than thelower limit, it is possible to select a material with a high refractiveindex. Thus, while achieving reduction in size and high magnification,it becomes easy to satisfactorily suppress fluctuation in variousaberrations during zooming. By not allowing the result of ConditionalExpression (1) to be equal to or greater than the upper limit, it ispossible to select a low dispersion material. Thus, it becomes easy tosatisfactorily suppress fluctuation in chromatic aberration duringzooming.

By not allowing the result of Conditional Expression (2) to be equal toor less than the lower limit, it is possible to select a low dispersionmaterial. Thus, it becomes easy to satisfactorily suppress fluctuationin chromatic aberration during zooming. By not allowing the result ofConditional Expression (2) to be equal to or greater than the upperlimit, it is possible to select a material with a high refractive index.Thus, while achieving reduction in size and high magnification, itbecomes easy to satisfactorily suppress fluctuation in variousaberrations during zooming. In addition, in a case of a configuration inwhich Conditional Expression (2-1) is satisfied, it is possible toobtain more favorable characteristics.45<νdn<55  (2-1)

By satisfying Conditional Expression (3), it becomes easy tosatisfactorily suppress fluctuation in secondary chromatic aberrationduring zooming. In addition, in a case of a configuration in whichConditional Expression (3-1) is satisfied, it is possible to obtain morefavorable characteristics.0.637<θgFn+0.001625×νdn<0.65  (3-1)

By satisfying Conditional Expressions (1) and (2) and by not allowingthe result of Conditional Expression (4) to be equal to or less than thelower limit, while achieving reduction in size and high magnification,it becomes easy to satisfactorily suppress fluctuation in variousaberrations including chromatic aberration during zooming. In order toselect a suitable material satisfying Conditional Expressions (1) and(2) from existing optical materials, it is preferable to satisfyConditional Expression (4-1).2.21<Ndn+0.01×νdn<2.33  (4-1)

For example, in the example shown in FIG. 1, the lens L2 d of the secondlens group G2 corresponds to the LN lens LN. However, in the zoom lensof the present invention, the LN lens LN may be different from theexample shown in FIG. 1.

Among the movable lens groups having negative refractive powers in themiddle group Gm, it is preferable that the movable lens group having thestrongest negative refractive power includes the LN lens LN. In such acase, it becomes easy to suppress fluctuation in chromatic aberrationduring zooming.

Further, it is preferable that the movable lens group (second lens groupG2 in the example shown in FIG. 1), which has the negative refractivepower in the middle group Gm, closer to the object side than the movablelens group (third lens group G3 in the example shown in FIG. 1), whichhas the negative refractive power and is closest to the image side inthe middle group Gm, includes the LN lens LN. In such a case, it ispossible to satisfactorily suppress fluctuation in lateral chromaticaberration during zooming from the wide-angle end to the middle zoomrange.

The movable lens group, which has the negative refractive power in themiddle group Gm, closer to the object side than the movable lens group,which has the negative refractive power and is closest to the image sidein the middle group Gm, includes the LN lens LN. In this configuration,assuming that a focal length of the movable lens group which has thenegative refractive power in the middle group and includes the LN lensLN, which has a strongest negative refractive power among the LN lensesLN, which are included in the movable lens group having the negativerefractive power in the middle group Gm and being located to be closerto the object side than the movable lens group, which has the negativerefractive power and is closest to the image side in the middle groupGm, is fA, and a focal length of the movable lens group, which has thenegative refractive power and is closest to the image side in the middlegroup Gm, is fB, it is preferable to satisfy Conditional Expression (5).By not allowing the result of Conditional Expression (5) to be equal toor less than the lower limit, it is possible to ensure the effect ofcorrecting the longitudinal chromatic aberration and the lateralchromatic aberration during zooming through the LN lens LN. As a result,it becomes easy to suppress these aberrations during zooming. By notallowing the result of Conditional Expression (5) to be equal to orgreater than the upper limit, it is possible to prevent the negativerefractive power of the lens group including the LN lens LN frombecoming excessively strong. As a result, it becomes easy to suppressfluctuation in longitudinal chromatic aberration and lateral chromaticaberration during zooming. In addition, in a case of a configuration inwhich Conditional Expression (5-1) is satisfied, it is possible toobtain more favorable characteristics.0.6<fB/fA<4.5  (5)2<fB/fA<4  (5-1)

Further, the movable lens group, which has the negative refractive powerin the middle group Gm, closer to the object side than the movable lensgroup, which has the negative refractive power and is closest to theimage side in the middle group Gm, includes the LN lens LN. In thisconfiguration, assuming that a focal length of the movable lens groupwhich has the negative refractive power in the middle group and includesthe LN lens LN, which has a strongest negative refractive power amongthe LN lenses LN, which are included in the movable lens group havingthe negative refractive power in the middle group Gm and being locatedto be closer to the object side than the movable lens group, which hasthe negative refractive power and is closest to the image side in themiddle group Gm, is fA, and a focal length of the LN lens LN, which hasthe strongest negative refractive power, among the LN lenses LN, whichare included in the movable lens group having the negative refractivepower in the middle group Gm, is fLNm, it is preferable to satisfyConditional Expression (6). By satisfying Conditional Expression (6), itbecomes easy to satisfactorily suppress fluctuation in primary chromaticaberration and fluctuation in secondary chromatic aberration duringzooming. In addition, in a case of a configuration in which ConditionalExpression (6-1) is satisfied, it is possible to obtain more favorablecharacteristics.0.5<fLNm/fA<40  (6)0.5<fLNm/fA<4  (6-1)

Further, it is preferable that the at least one movable lens group inthe middle group Gm includes a cemented lens in which at least one LNlens LN and at least one positive lens are cemented. In such a case, itbecomes easy to suppress fluctuation in chromatic aberration duringzooming. It should be noted that the cemented lens described herein maybe a cemented lens consisting of two lenses or a cemented lensconsisting of three lenses.

In the configuration in which the at least one movable lens group in themiddle group Gm includes a cemented lens in which at least one LN lensLN and at least one positive lens are cemented, assuming that an Abbenumber of the at least one LN lens LN of the cemented lens based on thed line is νdcn, and an Abbe number of at least one positive lens of thecemented lens based on the d line is νdcp, it is preferable that atleast one of the cemented lenses satisfies Conditional Expression (7).Here, it is assumed that the LN lens LN and the positive lens satisfyingConditional Expression (7) are lenses in the same cemented lens. Bysatisfying Conditional Expression (7), it becomes easy to satisfactorilysuppress fluctuation in primary chromatic aberration during zooming.18<νdcn−νdcp<35  (7)

It is preferable that the first lens group G1 includes a focus groupwhich is a lens group that moves during focusing. That is, it ispreferable that focusing is performed by moving at least a part oflenses in the first lens group G1 along the optical axis Z. Since thefirst lens group G1 does not move during zooming, in a case where atleast a part of the lenses in the first lens group G1 is used as thefocus group, the image point of the focus group does not move duringzooming. Therefore, focus shift during zooming can be suppressed.

It is preferable that the movable lens group closest to the image sidein the middle group Gm has a negative refractive power. In such a case,in a case of correcting fluctuation in image position during zooming, itis possible to move the movable lens group to the image side from thetelephoto side, and it becomes easy to ensure the zoom stroke of themovable lens group mainly responsible for the zooming function. As aresult, there is an advantage in reduction in size and highmagnification.

The middle group Gm and the subsequent group Gs can have, for example,the configurations described below. The middle group Gm can beconfigured to consist of the two movable lens groups having the negativerefractive powers. The subsequent group Gs can be configured to consistof a lens group which includes the aperture stop St, remains stationarywith respect to the image plane Sim during zooming, and has a positiverefractive power. In such a case, the zoom stroke of the movable lensgroup is reduced, and the total length of the lens system can beshortened. Therefore, there is an advantage in reduction in size.

Alternatively, the middle group Gm can be configured to consist of thetwo movable lens groups having the negative refractive powers. Inaddition, the subsequent group Gs can be configured to consist of, inorder from the object side to the image side, a lens group, whichincludes the aperture stop St, moves along the optical axis Z bychanging a distance between the groups adjacent to each other duringzooming, and has a positive refractive power, and a lens group whichremains stationary with respect to the image plane Sim and has apositive refractive power. In such a case, it becomes easy to achievereduction in size, high magnification, and suppression of fluctuation invarious aberrations during zooming. In addition, in the middle zoomrange where the off-axis ray is the highest, the movable lens grouphaving a positive refractive power including the aperture stop St can beextended to the object side. Thus, the lens diameter of the first lensgroup G1 can be suppressed. As a result, there is an advantage inachieving reduction in size of the first lens group G1.

Alternatively, the middle group Gm can be configured to consist of, inorder from the object side to the image side, the movable lens grouphaving a positive refractive power and the two movable lens groupshaving the negative refractive powers. In addition, the subsequent groupGs can be configured to consist of a lens group which includes theaperture stop St, remains stationary with respect to the image plane Simduring zooming, and has a positive refractive power. In such a case, itbecomes easy to achieve reduction in size, high magnification, andsuppression of fluctuation in various aberrations during zooming. Inparticular, there is an advantage in suppressing fluctuation inspherical aberration during zooming.

Alternatively, the middle group Gm can be configured to consist of thethree movable lens groups having the negative refractive powers. Inaddition, the subsequent group Gs can be configured to consist of a lensgroup which includes the aperture stop St, remains stationary withrespect to the image plane Sim during zooming, and has a refractivepower. In such a case, it becomes easy to achieve reduction in size,high magnification, and suppression of fluctuation in variousaberrations during zooming. In particular, there is an advantage insuppressing fluctuation in field curvature during zooming.

Alternatively, the middle group Gm can be configured to consist of thefour movable lens groups having the negative refractive powers. Inaddition, the subsequent group Gs can be configured to consist of a lensgroup which includes the aperture stop St, remains stationary withrespect to the image plane Sim during zooming, and has a positiverefractive power. In such a case, it becomes easy to achieve reductionin size, high magnification, and suppression of fluctuation in variousaberrations during zooming. In particular, there are advantages insuppressing fluctuation in field curvature and fluctuation in sphericalaberration during zooming.

The above-mentioned preferred configurations and availableconfigurations may be optional combinations, and it is preferable toselectively adopt the configurations in accordance with requiredspecification. According to the technology of the present invention, itis possible to realize a zoom lens having high optical performance bysuppressing fluctuation in chromatic aberration and fluctuation inspherical aberration during zooming.

Next, numerical examples of the zoom lens of the present invention willbe described.

Example 1

FIG. 1 is a cross-sectional view of a zoom lens of Example 1, and anillustration method and a configuration thereof is as described above.Therefore, repeated description is partially omitted herein. The zoomlens of Example 1 consists of, in order from the object side to theimage side, a first lens group G1 having a positive refractive power, asecond lens group G2 having a negative refractive power, a third lensgroup G3 having a negative refractive power, and a fourth lens group G4having a positive refractive power. The middle group Gm consists of asecond lens group G2 and a third lens group G3. The subsequent group Gsconsists of a fourth lens group G4. During zooming, the first lens groupG1 and the fourth lens group G4 remain with respect to the image planeSim, and the second lens group G2 and the third lens group G3 move alongthe optical axis Z by changing the distance between the lenses adjacentto each other.

The first lens group G1 consists of eleven lenses L1 a to L1 k in orderfrom the object side to the image side. The second lens group G2consists of six lenses L2 a to L2 f in order from the object side to theimage side. The third lens group G3 consists of two lenses L3 a and L3 bin order from the object side to the image side. The fourth lens groupG4 consists of an aperture stop St and nine lenses L4 a to L4 i in orderfrom the object side to the image side. The lens L2 d corresponds to theLN lens LN. The focus group consists of the lens L1 e.

Tables 1A and 1B show basic lens data of the zoom lens of Example 1,Table 2 shows values of specification and variable surface distances,and Table 3 shows aspheric surface coefficients thereof. Tables 1A and1B show the basic lens data which is divided into two tables in order toprevent one table from becoming long. In Tables 1A and 1B, the column ofSn shows surface numbers. The surface closest to the object side is thefirst surface, and the surface numbers increase one by one toward theimage side. The column of R shows radii of curvature of the respectivesurfaces. The column of D shows surface distances on the optical axisbetween the respective surfaces and the surfaces adjacent to the imageside. Further, the column of Nd shows a refractive index of eachconstituent element at the d line, the column of νd shows an Abbe numberof each constituent element at the d line, and the column of θgF shows apartial dispersion ratio of each constituent element between the g lineand the F line.

In Tables 1A and 1B, the sign of the radius of curvature of the surfaceconvex toward the object side is positive and the sign of the radius ofcurvature of the surface convex toward the image side is negative. Table1B also shows the aperture stop St and the optical member PP, and in aplace of a surface number of a surface corresponding to the aperturestop St, the surface number and a term of (St) are noted. A value at thebottom place of D in Table 1B indicates a distance between the imageplane Sim and the surface closest to the image side in the table. InTables 1A and 1B, the variable surface distances during zooming arereferenced by the reference signs DD[ ], and are written into places ofD, where object side surface numbers of distances are noted in[ ].

In the range of Table 2, values of the zoom ratio Zr, the focal lengthf, the F number FNo, the maximum total angle of view 2ω, and thevariable surface distance are based on the d line. (°) in the place of2ω indicates that the unit thereof is a degree. In Table 2, the valuesat the wide-angle end state, the middle focal length state, and thetelephoto end state are shown in the columns denoted as the wide-angleend, the middle, and the telephoto end, respectively.

In Tables 1A and 1B, the reference sign * is attached to surface numbersof aspheric surfaces, and numerical values of the paraxial radius ofcurvature are written into the column of the radius of curvature of theaspheric surface. In Table 3, the row of Sn shows surface numbers of theaspheric surfaces, and the rows of KA and Am (m is an integer of 3 ormore) shows numerical values of the aspheric surface coefficients foreach aspheric surface. The “E±n” (n: an integer) in numerical values ofthe aspheric surface coefficients of Table 3 indicates “×10^(±n)”. KAand Am are the aspheric surface coefficients in the aspheric expressionrepresented by the following expression.Zd=C×h ²/{1+(1−KA×C ² ×h ²)^(1/2) }+ΣAm×h ^(m)Here, Zd is an aspheric surface depth (a length of a perpendicular froma point on an aspheric surface at height h to a plane that isperpendicular to the optical axis and contacts with the vertex of theaspheric surface),

h is a height (a distance from the optical axis to the lens surface),

C is an inverse of a paraxial radius of curvature, and

KA and Am are aspheric surface coefficients, and

Σ in the aspheric surface expression means the sum with respect to m.

In data of each table, a degree is used as a unit of an angle, and mm(millimeter) is used as a unit of a length, but appropriate differentunits may be used since the optical system can be used even in a casewhere the system is enlarged or reduced in proportion. Further, each ofthe following tables shows numerical values rounded off to predetermineddecimal places.

TABLE 1A Example 1 Sn R D Nd Vd θgF *1 112.05486 3.000 1.80610 33.270.5885 2 31.98770 20.484  *3 163.75867 2.000 1.62001 56.94 0.5453 450.75686 16.848  5 −64.36966 1.930 1.95375 32.32 0.5901 6 −140.689140.300 7 136.33230 5.960 1.82498 23.78 0.6200 8 −406.68444 0.750 9222.60173 9.083 1.55404 74.37 0.5415 10 −90.49986 4.440 11 357.472524.218 1.43875 94.66 0.5340 *12 −147.10239 3.338 13 −82.60972 1.8001.76754 46.51 0.5593 14 −197.76427 0.100 15 159.57415 1.800 1.9427229.30 0.6003 16 65.00119 17.474  1.41390 100.82 0.5337 17 −51.798020.120 18 1242.12695 6.068 1.41390 100.82 0.5337 19 −88.80350 0.100 2054.40497 5.153 1.72916 54.68 0.5445 21 120.29294 DD[21] 22 45.900840.800 2.00100 29.13 0.5995 23 16.12303 4.891 24 −33.55758 0.760 1.7612051.88 0.5484 25 29.53847 2.815 1.89286 20.36 0.6394 26 −138.61046 0.8101.72900 49.12 0.5574 27 68.65529 1.379 28 31.97684 5.510 1.60835 37.170.5858 29 −18.55230 0.800 1.81281 46.72 0.5572 30 −506.03976 DD[30] 31−36.15586 0.810 1.67165 57.92 0.5428 32 74.84462 2.029 1.83207 23.770.6202 33 115989.92673 DD[33]

TABLE 1B Example 1 Sn R D Nd νd θgF 34(St) ∞ 1.000 *35  51.49771 6.0001.79600 45.42 0.5726 36 60.00792 0.493 37 53.44026 7.430 1.64479 42.320.5725 38 −33.64933 1.000 2.00100 29.13 0.5995 39 −53.69581 34.500 40107.79016 3.386 1.90000 21.31 0.6271 41 −101.32017 0.500 42 42.629065.654 1.61345 60.64 0.5430 43 −53.96087 1.000 2.00100 29.13 0.5995 4425.77644 1.469 45 28.77031 8.312 1.49700 81.54 0.5375 46 −27.92269 1.0001.95375 32.32 0.5901 47 −86.24838 0.120 48 79.50526 5.528 1.48749 70.240.5301 49 −35.20170 0.200 50 ∞ 1.000 1.51633 64.14 0.5353 51 ∞ 33.0001.60859 46.44 0.5666 52 ∞ 13.200 1.51633 64.05 0.5346 53 ∞ 10.924

TABLE 2 Example 1 Wide-Angle End Middle Telephoto End Zr 1.00 5.00 12.55f 4.674 23.370 58.658 FNo. 1.85 1.85 2.67 2ω(°) 103.68 25.62 10.48DD[21] 0.770 37.777 46.988 DD[30] 47.124 3.721 7.103 DD[33] 7.873 14.2691.676

TABLE 3 Example 1 Sn 1 3 12 35 KA 1.0000000E+00 1.0000000E+00  1.0000000E+00  1.∞∞∞OE+∞ A4 6.9424288E−07 9.4978117E−07 1.5276922−06−4.5195518E−06 A6 1.3970788E−10 3.9460279E−11 −4.5152395−11−2.4748083E−10 A8 1.3125248E−13 −1.6897109E−12 −4.0992029−13  3.1340865E−11 A10 −1.4945516E−16 2.1275734E−15   1.3006196E−15−3.6167994E−13 A12 4.1665629E−20 −5.1302380E−18 −4.3658800−18  2.5782474E−15 A14 1.0059271E−23 1.1242107E−20  9.092G332E−21−1.1637871E−17 A16 −2.6663153E−27 −1.2271961E−23 −1.0914656E−23  3.1832939E−20 A18 −2.5136743E−30 6.3024808E−27   6.9501868E−27−4.7984110E−23 A20 7.5327294E−34 −1.1701477E−30 −1.8164208E−30  3.0558222E−26

FIG. 7 shows aberration diagrams in a state where an object at infinityis brought into focus through the zoom lens of Example 1. In FIG. 7, inorder from the left side, spherical aberration, astigmatism, distortion,and lateral chromatic aberration are shown. In FIG. 7, the upper partlabeled by WIDE-ANGLE END shows the zoom lens in the wide-angle endstate, the middle part labeled by MIDDLE shows the zoom lens in themiddle focal length state, the lower part labeled by TELEPHOTO END showsthe zoom lens in the telephoto end state. In the spherical aberrationdiagram, aberrations at the d line, the C line, the F line, and the gline are indicated by the solid line, the long dashed line, the shortdashed line, and the chain double-dashed line, respectively. In theastigmatism diagram, aberration in the sagittal direction at the d lineis indicated by the solid line, and aberration in the tangentialdirection at the d line is indicated by the short dashed line. In thedistortion diagram, aberration at the d line is indicated by the solidline. In the lateral chromatic aberration diagram, aberrations at the Cline, the F line, and the g line are respectively indicated by the longdashed line, the short dashed line, and the chain double-dashed line. Inthe spherical aberration diagram, FNo. indicates an F number. In theother aberration diagrams, ω indicates a half angle of view.

Symbols, meanings, description methods, and illustration methods of therespective data pieces according to Example 1 are the same as those inthe following examples unless otherwise noted. Therefore, in thefollowing description, repeated description will be omitted.

Example 2

FIG. 3 is a cross-sectional diagram illustrating a configuration of thezoom lens of Example 2. The zoom lens of Example 2 consists of, in orderfrom the object side to the image side, a first lens group G1 having apositive refractive power; a second lens group G2 having a negativerefractive power; a third lens group G3 having a negative refractivepower; a fourth lens group G4 having a negative refractive power; and afifth lens group G5 having a negative refractive power. The middle groupGm consists of a second lens group G2, a third lens group G3, and afourth lens group G4. The subsequent group Gs consists of a fifth lensgroup G5. During zooming, the first lens group G1 and the fifth lensgroup G5 remain with respect to the image plane Sim, and the second lensgroup G2, the third lens group G3, and the fourth lens group G4 movealong the optical axis Z by changing the distance between lens groupsadjacent to each other.

The first lens group G1 consists of five lenses L1 a to L1 e in orderfrom the object side to the image side. The second lens group G2consists of one lens L2 a. The third lens group G3 consists of fivelenses L3 a to L3 e in order from the object side to the image side. Thefourth lens group G4 consists of three lenses L4 a to L4 c in order fromthe object side to the image side. The fifth lens group G5 consists ofan aperture stop St and thirteen lenses L5 a to L5 m in order from theobject side to the image side. The lens L3 b corresponds to the LN lensLN. The focus group consists of lenses L1 c to L1 e.

Tables 4A and 4B show basic lens data of the zoom lens of Example 2,Table 5 shows specification and variable surface distances, Table 6shows aspheric surface coefficients, and FIG. 8 shows aberrationdiagrams in a state where the object at infinity is in focus.

TABLE 4A Example 2 Sn R D Nd νd θgF 1 5602.63981 3.000 1.80400 46.530.5578 2 156.50042 2.491 3 161.56661 15.000 1.43387 95.18 0.5373 4−494.65898 10.734 5 254.02818 8.441 1.43387 95.18 0.5373 6 −1596.367620.120 7 181.16407 8.366 1.43503 95.06 0.5365 8 1016.32141 0.120 9133.63070 13.433 1.43387 95.18 0.5373 10 −1805.13656 DD[10] 11−4033.62138 2.550 1.53775 74.70 0.5394 12 1218.32158 DD[12] *13−125.00012 1.100 1.94456 34.70 0.5839 14 22.63186 4.763 15 −81.203180.960 1.77520 54.61 0.5543 16 −91.56724 0.844 17 −48.17710 3.759 1.8913720.40 0.6393 18 −22.33171 0.960 1.89885 36.67 0.5792 19 199.75434 0.12020 61.18091 4.401 1.80895 29.00 0.6023 21 −63.07147 DD[21] 22 −73.712213.440 1.89899 20.07 0.6310 23 −34.32030 0.960 1.90000 37.99 0.5734 24−115.86534 0.973 25 −64.19666 0.960 1.87556 41.48 0.5662 26 −234.49168DD[26]

TABLE 4B Example 2 Sn R D Nd νd θgF 27 (St) ∞ 1.671 28 −1662.30529 5.3341.76385 48.49 0.5590 29 −53.40895 0.120 30 78.44936 8.677 1.66090 62.490.5426 31 −47.53906 1.200 1.91079 35.21 0.5818 32 −85.74047 4.781 3391.16381 5.360 1.58931 69.59 0.5407 34 −70.24529 1.280 1.90000 20.220.6306 35 636.76591 12.197 36 −53.31083 1.000 1.83473 44.49 0.5587 3758.25148 0.395 38 37.30208 3.087 1.89999 20.00 0.6313 39 69.35698 57.58440 567.67184 3.006 1.76047 27.03 0.6065 41 −83.27423 1.070 42 89.364481.054 1.88185 39.80 0.5710 43 27.03477 6.863 1.63365 63.66 0.5423 44−136.91445 1.011 45 −65.24557 5.942 1.48749 70.24 0.5301 46 −20.720721.314 1.83732 42.69 0.5651 47 −76.35609 0.320 48 150.81544 6.610 1.4874970.24 0.5301 49 −31.84760 0.000 50 ∞ 33.000 1.60859 46.44 0.5666 51 ∞13.200 1.51633 64.05 0.5346 52 ∞ 11.925

TABLE 5 Example 2 Wide-Angle End Middle Telephoto End Zr 1.00 10.5440.50 f 10.059 106.043 407.392 FNo. 2.06 2.06 3.85 2ω (°) 59.82 5.801.52 DD[10] 1.200 17.156 16.823 DD[12] 2.000 100.197 121.037 DD[21]136.547 8.603 8.884 DD[26] 7.576 21.367 0.579

TABLE 6 Example 2 Sn 13 KA 1.0000000E+00 A4 3.5830376E−06 A66.3192990E−08 A8 −2.1933635E−09 A10 4.2082595E−11 A12 −5.0799726−13 A143.8672311E−15 A16 −1.7902791E−17 A18 4.5886787E−20 A20 −4.9871907E−23

Example 3

FIG. 4 is a cross-sectional diagram illustrating a configuration of thezoom lens of Example 3. The zoom lens of Example 3 consists of, in orderfrom the object side to the image side, a first lens group G1 having apositive refractive power; a second lens group G2 having a negativerefractive power; a third lens group G3 having a negative refractivepower; a fourth lens group G4 having a negative refractive power; afifth lens group G5 having a negative refractive power; and a sixth lensgroup G6 having a positive refractive power. The middle group Gmconsists of a second lens group G2, a third lens group G3, a fourth lensgroup G4, and a fifth lens group G5. The subsequent group Gs consists ofa sixth lens group G6. During zooming, the first lens group G1 and thesixth lens group G6 remain with respect to the image plane Sim, and thesecond lens group G2, the third lens group G3, the fourth lens group G4,and the fifth lens group G5 move along the optical axis Z by changingthe distance between lens groups adjacent to each other.

The first lens group G1 consists of five lenses L1 a to L1 e in orderfrom the object side to the image side. The second lens group G2consists of one lens L2 a. The third lens group G3 consists of fourlenses L3 a to L3 d in order from the object side to the image side. Thefourth lens group G4 consists of two lenses L4 a and L4 b in order fromthe object side to the image side. The fifth lens group G5 consists oftwo lenses L5 a and L5 b in order from the object side to the imageside. The sixth lens group G6 consists of an aperture stop St and tenlenses L6 a to L6 j in order from the object side to the image side. Thelens L4 a corresponds to the LN lens LN. The focus group consists oflenses L1 c to L1 e.

Table 7 shows basic lens data of the zoom lens of Example 3, Table 8shows specification and variable surface distances, Table 9 showsaspheric surface coefficients, and FIG. 9 shows aberration diagrams in astate where the object at infinity is in focus.

TABLE 7 Example 3 Sn R D Nd νd θgF  1 2758.42359 2.980 1.80400 46.530.5578  2 152.67265 1.787  3 155.78881 15.000 1.43387 95.18 0.5373  4−579.43924 10.554  5 311.40157 6.877 1.43700 95.10 0.5336  6 −2543.961770.120  7 172.37716 10.400 1.43387 95.18 0.5373  8 ∞ 0.120  9 123.6828413.410 1.43387 95.18 0.5373  10 ∞ DD[10]  11 2719.51051 2.270 1.5503275.50 0.5400  12 526.89880 DD[12]  13 242.77714 1.050 2.00100 29.130.5995  14 23.20915 7.158  15 −62.97480 4.200 1.89286 20.36 0.6394  16−27.16300 1.010 1.89190 37.13 0.5781  17 262.01725 0.300  18 50.900263.904 1.92286 20.88 0.6390  19 −1873.94860 DD[19]  20 −88.84343 0.9101.76385 48.49 0.5590  21 157.11400 1.600 1.92286 20.88 0.6390  221415.06905 DD[22]  23 −64.30288 1.180 1.90043 37.37 0.5767  24 124.490003.410 1.89286 20.36 0.6394  25 −223.30610 DD[25]  26 (St) ∞ 1.000  2773.95141 8.154 1.76385 48.49 0.5590 *28 −55.93924 0.171  29 65.498498.290 1.43875 94.66 0.5340  30 −47.73600 1.240 1.95906 17.47 0.6599  31−128.25888 3.375 *32 −100.54918 1.000 1.80610 40.93 0.5702  33 53.986720.399  34 49.88468 2.736 1.95906 17.47 0.6599  35 89.66151 44.161  36118.02446 3.680 1.85478 24.80 0.6123  37 −118.02446 1.019  38 41.730808.310 2.00100 29.13 0.5995  39 21.41900 12.300 1.48749 70.24 0.5301  40−21.41900 0.980 1.91082 35.25 0.5822  41 116.06433 7.692  42 269.356845.898 1.56883 56.04 0.5485  43 −27.85993 0.200  44 ∞ 1.000 1.51633 64.140.5353  45 ∞ 33.000 1.60859 46.44 0.5666  46 ∞ 13.200 1.51633 64.050.5346  47 ∞ 13.497

TABLE 8 Example 3 Wide-Angle End Middle Telephoto End Zr 1.00 10.5444.34 f 9.603 101.230 425.814 FNo. 2.06 2.06 4.04 2ω (°) 62.36 6.12 1.46DD[10] 1.200 40.215 38.966 DD[12] 1.200 69.899 92.346 DD[19] 49.2852.025 10.563 DD[22] 96.090 15.175 5.023 DD[25] 1.198 21.660 2.075

TABLE 9 Example 3 Sn 28 32 KA   1.0000000E+00 1.0000000E+00 A4 12726760E−06 4.7415505E−07 A6   3.6654463E−09 6.5877762E−09 A8−3.2814800E−11 −6.9216211E−11 A10   1.9124227E−13 4.3338142E−13 A12−8.0478127E−16 −1.9572115E−15 A14   2.3664959E−18 6.5784048E−18 A16−4.5218264E−21 −1.5503257E−20 A18   4.9870538E−24 2.2423809E−23 A20−2.3905900E−27 −1.4628348E−26

Example 4

FIG. 5 is a cross-sectional diagram illustrating a configuration of thezoom lens of Example 4. The zoom lens of Example 4 consists of, in orderfrom the object side to the image side, a first lens group G1 having apositive refractive power; a second lens group G2 having a positiverefractive power; a third lens group G3 having a negative refractivepower; a fourth lens group G4 having a negative refractive power; and afifth lens group G5 having a positive refractive power. The middle groupGm consists of a second lens group G2, a third lens group G3, and afourth lens group G4. The subsequent group Gs consists of a fifth lensgroup G5. During zooming, the first lens group G1 and the fifth lensgroup G5 remain with respect to the image plane Sim, and the second lensgroup G2, the third lens group G3, and the fourth lens group G4 movealong the optical axis Z by changing the distance between lens groupsadjacent to each other.

The first lens group G1 consists of ten lenses L1 a to L1 j in orderfrom the object side to the image side. The second lens group G2consists of one lens L2 a. The third lens group G3 consists of fivelenses L3 a to L3 e in order from the object side to the image side. Thefourth lens group G4 consists of two lenses L4 a and L4 b in order fromthe object side to the image side. The fifth lens group G5 consists ofan aperture stop St and twelve lenses L5 a to L51 in order from theobject side to the image side. The lens L3 d corresponds to the LN lensLN. The focus group consists of the lens L1 e.

Tables 10A and 10B show basic lens data of the zoom lens of Example 4,Table 11 shows specification and variable surface distances, Table 12shows aspheric surface coefficients, and FIG. 10 shows aberrationdiagrams in a state where the object at infinity is in focus.

TABLE 10A Example 4 Sn R D Nd νd θgF 1 212.64499 6.254 1.88300 40.760.5668 2 74.86592 23.869 3 −627.85865 3.300 1.73400 51.47 0.5487 4415.23299 11.658 5 −188.89629 6.507 1.53775 74.70 0.5394 6 120.9898015.785 1.91650 31.60 0.5912 7 −1261.04953 2.372 *8 341.42320 14.1411.43875 94.94 0.5343 9 −172.58167 13.476 10 196.27510 16.727 1.4970081.54 0.5375 11 −142.13691 0.746 12 −133.96197 3.835 1.85150 40.780.5696 13 115.40048 15.239 1.49700 81.54 0.5375 14 −398.54695 5.967 15476.04931 13.278 1.53775 74.70 0.5394 16 −156.68439 0.200 17 138.7259815.823 1.49700 81.54 0.5375 18 −263.84403 DD[18] 19 366.99360 2.9771.49700 81.54 0.5375 20 −561.66067 DD[20] *21 226.22641 2.545 1.5377574.70 0.5394 22 27.32961 10.437 23 −42.81716 1.200 2.00100 29.13 0.599524 205.22485 2.383 25 −107.19469 6.281 1.76182 26.52 0.6136 26 −32.331192.429 1.76385 48.49 0.5590 27 −82.93832 0.830 28 164.41669 5.230 1.8348142.72 0.5649 29 −80.33728 DD[29] 30 −52.83733 1.310 1.49700 81.54 0.537531 1463.88443 1.966 1.84666 23.83 0.6160 32 −302.51705 DD[32]

TABLE 10B Example 4 Sn R D Nd νd θgF 33 (St) ∞ 1.167 34 118.97527 3.8301.91082 35.25 0.5822 35 −331.85890 1.578 36 −104.55957 3.000 1.7618226.52 0.6136 37 −211.28070 9.936 38 60.09505 5.271 1.65844 50.88 0.556139 ∞ 1.417 40 42.26187 10.113 1.43875 94.94 0.5343 41 −78.18443 2.0591.95375 32.32 0.5901 42 56.33405 4.832 43 −226.33060 6.273 1.80518 25.430.6103 44 −36.25955 1.410 1.80400 46.58 0.5573 45 −107.11379 0.200 4664.21220 7.806 1.48749 70.24 0.5301 47 −64.21220 0.200 48 53.82475 1.9731.91082 35.25 0.5822 49 20.50244 14.037 1.49700 81.54 0.5375 50−41.82031 1.601 1.90043 37.37 0.5772 51 57.48527 0.615 52 48.65119 3.3131.84666 23.83 0.6160 53 240.54111 3.000 54 ∞ 5.090 1.51633 64.14 0.535355 ∞ 53.873

TABLE 11 Example 4 Wide-Angle End Middle Telephoto End Zr 1.00 2.35 7.35f 19.904 46.795 146.298 FNo. 2.86 2.86 2.86 2ω (°) 72.68 32.72 10.84DD[18] 1.500 50.247 86.698 DD[20] 1.493 6.843 8.752 DD[29] 64.090 9.41621.406 DD[32] 52.724 53.301 2.952

TABLE 12 Example 4 Sn 8 KA 1.0000000E+00 A3 1.5064530E−07 A4−1.5641141E−07 A5 1.6501598E−09 A6 −3.9701428E−11 A7 6.9263338E−13 A81.0556630E−17 A9 −7.0509369E−17 A10 5.3287613E−19 Sn 21 KA 1.0000000E+00A4 1.5045420E−06 A6 −4.1679388E−10 A8 −8.9800509E−12 A10 7.0993908E−14A12 −3.2299521E−16 A14 8.7823289E−19 A16 −1.4036759E−21 A181.2097861E−24 A20 −4.3023907E−28

Example 5

FIG. 6 is a cross-sectional diagram illustrating a configuration of thezoom lens of Example 5. The zoom lens of Example 5 consists of, in orderfrom the object side to the image side, a first lens group G1 having apositive refractive power; a second lens group G2 having a negativerefractive power; a third lens group G3 having a negative refractivepower; a fourth lens group G4 having a positive refractive power; and afifth lens group G5 having a positive refractive power. The middle groupGm consists of a second lens group G2 and a third lens group G3. Thesubsequent group Gs consists of a fourth lens group G4 and a fifth lensgroup G5. During zooming, the first lens group G1 and the fifth lensgroup G5 remain with respect to the image plane Sim, and the second lensgroup G2, the third lens group G3, and the fourth lens group G4 movealong the optical axis Z by changing the distance between lens groupsadjacent to each other.

The first lens group G1 consists of six lenses L1 a to L1 f in orderfrom the object side to the image side. The second lens group G2consists of six lenses L2 a to L2 f in order from the object side to theimage side. The third lens group G3 consists of two lenses L3 a and L3 bin order from the object side to the image side. The fourth lens groupG4 consists of an aperture stop St and four lenses L4 a to L4 d in orderfrom the object side to the image side. The fifth lens group G5 consistsof six lenses L5 a to L5 f in order from the object side to the imageside. The lens L2 b corresponds to the LN lens LN. The first focus groupconsists of the lenses L1 d to L1 e, and the second focus group consistsof the lens L1 f. During focusing, the first focus group and the secondfocus group move along the optical axis Z with different loci from eachother.

Table 13 shows basic lens data of the zoom lens of Example 5, Table 14shows specification and variable surface distances, Table 15 showsaspheric surface coefficients, and FIG. 11 shows aberration diagrams ina state where the object at infinity is in focus.

TABLE 13 Example 5 Sn R D Nd νd θgF  1 −156.56421 2.000 1.80610 33.270.5885  2 221.88779 1.481  3 237.53179 11.070 1.43387 95.18 0.5373  4−168.43113 0.120  5 373.95224 6.920 1.43700 95.10 0.5336  *6 −275.485807.246  7 148.64138 8.140 1.43387 95.18 0.5373  8 −485.06373 0.120  9125.26147 9.870 1.43700 95.10 0.5336  10 −257.81028 0.600  11 57.605314.790 1.76385 48.49 0.5590  12 91.88531 DD[12] *13 79.37067 0.9002.00099 28.39 0.6018  14 14.28492 5.866  15 −44.16134 0.710 1.7960045.42 0.5726  16 179.98246 6.183 1.91379 19.31 0.6467  17 −13.954710.700 2.00001 28.00 0.6031  18 175.18740 0.120  19 35.61909 3.8921.67780 31.59 0.6002  20 −58.67291 0.730 1.80591 47.41 0.5559  21−337.80693 DD[21]  22 −29.80390 0.750 1.92480 35.52 0.5818  23 65.121472.161 2.00000 17.11 0.6644  24 −179.08021 DD[24]  25 (St) ∞ 2.111  26−223.75130 3.599 1.79304 48.70 0.5534  27 −43.84467 0.120  28 180.602242.111 1.78332 49.67 0.5516  29 −249.99472 0.948  30 61.25346 7.2611.51000 63.83 0.5353  31 −47.11201 0.920 1.94355 33.64 0.5866  32−872.08930 DD[32]  33 844.60059 3.080 1.73800 32.33 0.5900  34 −59.186654.322  35 41.48104 5.440 1.48749 70.24 0.5301  36 −49.50700 0.8601.95375 32.32 0.5901  37 33.85248 1.342  38 40.17043 7.500 1.53775 74.700.5394  39 −26.65900 0.880 1.87070 40.73 0.5683  40 −80.58184 1.244  4176.68452 6.239 1.58144 40.75 0.5776  42 −43.96715 0.200  43 ∞ 1.0001.52780 58.67 0.5539  44 ∞ 33.000 1.60859 46.44 0.5666  45 ∞ 13.2001.51633 64.05 0.5346  46 ∞ 10.787

TABLE 14 Example 5 Wide-Angle End Middle Telephoto End Zr 1.00 7.3823.11 f 8.095 59.739 187.068 FNo. 1.89 1.89 2.96 2ω (°) 73.72 10.30 3.32DD[12] 1.036 44.031 52.380 DD[21] 51.312 2.948 3.066 DD[24] 10.09914.288 1.393 DD[32] 34.796 35.976 40.405

TABLE 15 Example 5 Sn 6 13 KA 1.0000000E+00  1∞∞∞OE+00 A4 1.0052940E−074.8215119E−06 A6 5.1522150E−11 −2.3555604E−08   A8 −1.7490134E−136.0363095−10 A10 3.7973078E−16 −1.7467297−11   A12 −4.8615002E−193.4205709E−13 A14 3.8280238E−22 −3.8657172E−15   A16 −1.8028238E−252.4362214E−17 A18 4.5969112E−29 −7.9834448E−20   A20 −4.7850097E−331.0600242E−22

Table 16 shows values corresponding to Conditional Expressions (1) to(7) of the zoom lenses of Examples 1 to 5. Examples 1 to 5 are based onthe d line. Table 16 shows the values on the d line basis.

TABLE 16 Expression Number Example 1 Example 2 Example 3 Example 4Example 5 (1) Ndn 1.72900 1.77520 1.76385 1.76385 1.79600 (2) νdn 49.1254.61 48.49 48.49 45.42 (3) θgFn + 0.001625 × νdn 0.6372 0.6430 0.63780.6378 0.6464 (4) Ndn + 0.01 × νdn 2.220 2.321 2.249 2.249 2.250 (5)fB/fA 3.74 2.83 0.83 2.92 2.81 (6) fLNm/fA 3.9 39.3 0.6 1.3 3.0 (7) νdcn− νdcp 28.76 — 27.61 21.97 26.11

As can be seen from the above data, the zoom lenses of Examples 1 to 5each are miniaturized, have high magnification which is a magnificationof 7 or more, and have high optical performance by suppressingfluctuation in chromatic aberration and fluctuation in sphericalaberration during zooming and satisfactorily correcting variousaberrations.

Next, an imaging apparatus according to an embodiment of the presentinvention will be described. FIG. 12 is a schematic configurationdiagram of an imaging apparatus 100 using the zoom lens 1 according tothe above-mentioned embodiment of the present invention as an example ofan imaging apparatus of an embodiment of the present invention. Examplesof the imaging apparatus 100 include a broadcast camera, a movie imagingcamera, a video camera, a surveillance camera, and the like.

The imaging apparatus 100 comprises a zoom lens 1, a filter 2 which isdisposed on the image side of the zoom lens 1, and an imaging element 3which is disposed on the image side of the filter 2. FIG. 12schematically show a plurality of lenses provided in the zoom lens 1.

The imaging element 3 converts an optical image, which is formed throughthe zoom lens 1, into an electrical signal. For example, it is possibleto use a charge coupled device (CCD), complementary metal oxidesemiconductor (CMOS), or the like. The imaging element 3 is disposedsuch that the imaging surface thereof is coplanar with the image planeof the zoom lens 1.

The imaging apparatus 100 also comprises a signal processing section 5which performs calculation processing on an output signal from theimaging element 3, a display section 6 which displays an image formed bythe signal processing section 5, and a zoom control section 7 whichcontrols zooming of the zoom lens 1. Although only one imaging element 3is shown in FIG. 12, a so-called three-plate imaging apparatus havingthree imaging elements may be used.

The technology of the present invention has been hitherto describedthrough embodiments and examples, but the technology of the presentinvention is not limited to the above-mentioned embodiments andexamples, and may be modified into various forms. For example, valuessuch as the radius of curvature, the surface distance, the refractiveindex, the Abbe number, and the aspheric surface coefficient of eachlens are not limited to the values shown in the numerical examples, anddifferent values may be used therefor.

What is claimed is:
 1. A zoom lens consisting of, in order from anobject side to an image side: a first lens group that remains stationarywith respect to an image plane during zooming and has a positiverefractive power; a middle group that consists of two or more movablelens groups moving along an optical axis by changing a distance betweengroups adjacent to each other during zooming; and a subsequent groupthat has a lens group including a stop at a position closest to theobject side, wherein at least two movable lens groups in the middlegroup each have a negative refractive power, wherein the at least onemovable lens group having the negative refractive power in the middlegroup includes at least one LN lens which is a negative lens, andwherein assuming that a refractive index of the LN lens at a d line isNdn, an Abbe number of the LN lens based on the d line is νdn, and apartial dispersion ratio of the LN lens between a g line and an F lineis θgFn, the LN lens satisfies Conditional Expressions (1), (2), (3),and (4) represented by1.72<Ndn<1.8  (1),43<νdn<57  (2),0.6355<θgFn+0.001625×νdn<0.66  (3), and2.21<Ndn+0.01×νdn  (4).
 2. The zoom lens according to claim 1, whereinthe movable lens group, which has the negative refractive power in themiddle group, closer to the object side than the movable lens group,which has the negative refractive power and is closest to the image sidein the middle group, includes the LN lens, and wherein assuming that afocal length of the movable lens group which has the negative refractivepower in the middle group and includes the LN lens, which has astrongest negative refractive power among the LN lenses, which areincluded in the movable lens group having the negative refractive powerin the middle group and being located to be closer to the object sidethan the movable lens group, which has the negative refractive power andis closest to the image side in the middle group, is fA, and a focallength of the movable lens group, which has the negative refractivepower and is closest to the image side in the middle group, is fB,Conditional Expression (5) is satisfied, which is represented by0.6<fB/fA<4.5  (5).
 3. The zoom lens according to claim 2, whereinConditional Expression (5-1) is satisfied, which is represented by2<fB/fA<4  (5-1).
 4. The zoom lens according to claim 1, wherein themovable lens group, which has the negative refractive power in themiddle group, closer to the object side than the movable lens group,which has the negative refractive power and is closest to the image sidein the middle group, includes the LN lens, and wherein assuming that afocal length of the movable lens group which has the negative refractivepower in the middle group and includes the LN lens, which has astrongest negative refractive power among the LN lenses, which areincluded in the movable lens group having the negative refractive powerin the middle group and being located to be closer to the object sidethan the movable lens group, which has the negative refractive power andis closest to the image side in the middle group, is fA, and a focallength of the LN lens, which has the strongest negative refractivepower, among the LN lenses, which are included in the movable lens grouphaving the negative refractive power in the middle group, is fLNm,Conditional Expression (6) is satisfied, which is represented by0.5<fLNm/fA<40  (6).
 5. The zoom lens according to claim 4, whereinConditional Expression (6-1) is satisfied, which is represented by0.5<fLNm/fA<4  (6-1).
 6. The zoom lens according to claim 1, wherein theat least one movable lens group in the middle group includes a cementedlens in which at least one LN lens and at least one positive lens arecemented.
 7. The zoom lens according to claim 6, wherein assuming thatan Abbe number of the at least one LN lens of the cemented lens based onthe d line is νdcn, and an Abbe number of at least one positive lens ofthe cemented lens based on the d line is νdcp, at least one of thecemented lenses satisfies Conditional Expression (7) represented by18<νdcn−νdcp<35  (7).
 8. The zoom lens according to claim 1, wherein themovable lens group having the strongest negative refractive power amongthe movable lens groups having the negative refractive powers in themiddle group includes the LN lens.
 9. The zoom lens according to claim1, wherein focusing is performed by moving at least a part of lenses inthe first lens group along the optical axis.
 10. The zoom lens accordingto claim 1, wherein the movable lens group closest to the image side inthe middle group has a negative refractive power.
 11. The zoom lensaccording to claim 10, wherein the middle group consists of the twomovable lens groups having the negative refractive powers, and whereinthe subsequent group consists of a lens group which remains stationarywith respect to the image plane during zooming and has a positiverefractive power.
 12. The zoom lens according to claim 10, wherein themiddle group consists of the two movable lens groups having the negativerefractive powers, and wherein the subsequent group consists of, inorder from the object side to the image side, a lens group, which movesalong the optical axis by changing a distance between the groupsadjacent to each other during zooming and has a positive refractivepower, and a lens group which remains stationary with respect to theimage plane during zooming and has a positive refractive power.
 13. Thezoom lens according to claim 10, wherein the middle group consists of,in order from the object side to the image side, the movable lens grouphaving a positive refractive power and the two movable lens groupshaving the negative refractive powers, and wherein the subsequent groupconsists of a lens group which remains stationary with respect to theimage plane during zooming and has a positive refractive power.
 14. Thezoom lens according to claim 10, wherein the middle group consists ofthe three movable lens groups having the negative refractive powers, andwherein the subsequent group consists of a lens group which remainsstationary with respect to the image plane during zooming and has arefractive power.
 15. The zoom lens according to claim 10, wherein themiddle group consists of the four movable lens groups having thenegative refractive powers, and wherein the subsequent group consists ofa lens group which remains stationary with respect to the image planeduring zooming and has a positive refractive power.
 16. The zoom lensaccording to claim 1, wherein the LN lens further satisfies ConditionalExpression (2-1) represented by45<νdn<55  (2-1).
 17. The zoom lens according to claim 1, wherein the LNlens further satisfies Conditional Expression (3-1) represented by0.637<θgFn+0.001625×νdn<0.65  (3-1).
 18. The zoom lens according toclaim 1, wherein the LN lens further satisfies Conditional Expression(4-1) represented by2.21<Ndn+0.01×νdn<2.33  (4-1).
 19. An imaging apparatus comprising thezoom lens according to claim 1.